1. Field of the Invention
The present invention relates to a metallic catalyst support for use in supporting catalyst for combustion and, more particularly, to a metallic catalyst support composed of a heat resistant metal provided with characteristics as a catalyst support.
2. Description of the Prior Art
Hitherto, in one of the environmental pollution control measures for automobiles, it has been conventional to interpose a ternary catalytic converter (catalytic converter rhodium) in a middle part of an exhaust pipe to purify the exhaust gas.
A metallic support of honeycomb construction has been known as one of such catalyst supports used in the converter. This metallic catalyst support comprises a corrugated plate and a flat plate each formed of a foil of 0.05 mm in thickness of heat resistant metal of the composition 20Cr-5Al, the said corrugated plate and flat plate being combined to form a core unit of multi-layer honeycomb construction by rolling or laminating them together.
To maintain the shape and construction of the core unit the, joint portions between the corrugated plate and the flat plate have been conventionally joined by brazing, spot-welding or laser welding an open end face thereof.
In the brazing method used most popularly as one of the mentioned joining methods, however, there is a disadvantage that not only the solder itself is expensive but also cost of the necessary equipment is high due to requirements such as vacuum, and high temperatures of not lower than 1000.degree. C. Further, the brazing method is not always efficient since it takes much labor and time, and all in all, it may be said that this brazing is the most expensive for manufacturing the core unit of honeycomb construction.
In the spot-welding or end face laser welding method, it becomes essential to apply a very precise weld to a plurality of portions of a foil of 0.05 mm in thickness with a pitch of 2 mm. Thus these welding methods have not only a disadvantage of poor working efficiency but also that of less welding reliability.
Moreover, since in any of the mentioned conventional methods where joining is partially carried out between one corrugated plate and another flat plate immediately adjacent to each other, if looking at the plurality of welded spots entirely, there arise disadvantages such that a center part of the core unit may appear like a bamboo shoot or some joined portions may be separated due to repetition of thermal deformation under high temperature. To overcome the above disadvantages, a joining method has been proposed in which retainer protrusions are disposed alternately at several points of the corrugated plate and flat plate rolled together, as disclosed in Japanese Laid-Open Patent Publications (unexamined) Nos. 25321/1979 and 236949/1989 and Japanese Laid-Open Utility Model Registration Publication (unexamined) No. 136735/1988.
In the joining method proposed in these publications, the corrugated plate and flat plate are not directly joined, but only an end part there-between is joined, or relative part is in contact with the retainer protrusions only. Accordingly, as a result of sharp heating to a high temperature, sharp cooling therefrom to a low temperature, and repetition of such sharp temperature changes, the relative retainer parts tend to loosen due to uneven expansion and shrinkage between the corrugated plate and flat plate moreover, the corrugated plate and the flat plate forming a core unit tend to be vibrated and rubbed against each other due to the exhaust gas passing through at high speed, thus resulting in getting out of the catalyst support and after all a decline in the catalytic performance.
A further attempt has been proposed in which principal part of a case or outer casing is provided with a stopper for preventing the core unit from getting out (Japanese Laid-Open Utility Model Registration Publication (unexamined) No. 78219/1989). However, any of these arrangements is not related to manufacturing and assembling of the core unit, but disclosed that a core unit is received in the outer casing provided with the mentioned stopper, and no technical advantage of overcoming the above problems is disclosed.